Suspension polymerization is used to make particles for molding plastics, for removing metal ions from aqueous feedstreams, and is especially used to make particles for chromatographic separation media. Suspension polymerization involves a dispersed monomer droplet phase in a dispersion media, wherein the dispersed monomer has a low solubility in the dispersion media, e.g., a discontinuous aqueous phase (droplet phase) in a continuous organic phase (dispersion media). In suspension polymerization, polymerization occurs in the droplet phase, which can impact particle size. Therefore, small amounts of stabilizer usually are added to stabilize the droplets and hinder coalescence. After polymerization, the particles are collected (e.g., via filtering) and washed.
The particle size in suspension polymerization is controlled by factors including for example, the agitation speed, the fraction of monomer phase, and the type and amount of stabilizer used. Suspension polymerization can result in a large distribution of particle size ranges and typically an additional step is needed to remove the suspended particles from the dispersion media. In addition, a classification step is often required to fractionate the particles into the desired size range. Because of the presence of two discrete, immiscible phases, one is often limited in terms of the components that can be incorporated into the monomer phase. For example, monomers or other additives such as porogens, which would partition into the dispersion media, cannot be effectively used. For these reasons, it is desirable to control the particle size and to have less process steps (i.e., a single phase polymerization).